Sesistance unit



Aug. 25, 1936. l Hl FENDER v 2,052,533

RESISTANCE UNIT Filed Dec; 8, 1933 4 Sheets-Sheet 1 L i 3 INVENTGR.

A TTORNEY.

RESISTANCE UNIT Aug. 25? i936' 4 sheets-Sheffc 2 Filed De0- 8 1933INVENTOR' fm @M` BY 'MXM m.\ mL.

ATTORNEY' Aug. 25, 1936. H. PE'NDER RESISTANCE UNIT 4 Sheets-Sheet 3INVENTOR.

Filed Dec. 8, 1953 Aug. 25, 1936. H. FENDER RESISTANCE UNIT 4Sheets-Sheet 4 Filed Dec. 8, 1933 INVENTOR.

#ma @Wm A TTORNEY.

Patented Aug. "25, 1936.

UNITED sucresl PATENT i OFFICE 2,052,533 I RESISTANCE UNIT HaroldPender, Mei-ion Township, Montgomery County, Pa.

Application December 8, 1933, Serial No. 701,471

' 9 claims. (ci. aol-1s) My invention relates to resistance units, ofgeneral application, and more particularly to those finding theirapplicationin radio receiving Viilamentary or rod-like element ofinsulating' material suchas glass, porcelain or other vitreous productcoated Iwith a resistance material, the

specific resistance of which may vary within wide limits in accordancewith the uses to which the unit is to be adapted, or the resistanceelement may comprise a molded body of any oi several well-known mixturesof conductive and insulating materials. Such resistance elements in genleral have a 'relatively high speciilc resistance which gives rise alsotoa relatively high contact resistance between the element and itsassociated terminal structures. This contact resistance may be not onlyrelatively high, but may tend to fluctuate substantially and rapidly,particularly when the resistance elem'ent has a hard and rough surface,giving rise to noises or disturbances'in the apparatus of which theresistance unit forms a part. My invention is directed primarily toresistance units of the above type in which provision is made forreducing to a minimum and maintaining substantially constant the contactresistance 'between the. terminal structure of the unit and theresistance element.

My invention resides also in new and improved methods of formingresistance .unitscf the type described above and to new and'iin- 40proved methods forensuring axsatisfactory contact between a resistanceelement and its termnal structure and to new and improved methods forpressure molding an insulating compound@ about a frangible resistanceelement.

My invention resides also in new and improved methods of formingresistanceunits of the type described above and to new and improvedmethods for ensuring a satisfactory contact between a resistance elementand its terminal structure 50 and to n'ew`andimprpved methods forpressure molding-an insulating compound about a fran' gible resistanceelement.

It is an object of my invention, therefore', to l provide ra new andimproved resistance unit which 55 is simple, missed and economical tomanufacture.

It is a still further object of my It is another object of my inventionto provide a new and improved resistance unit in which a frangibleresistance element is completely molded in and supported by a mass ofinsulating material. l

It is another object of my invention to provide anew and improvedresistance unit comprising a resistance element molded in a mass ofinsulating material in-which the parts projecting from the. moldedinsulation are reduced to a minimum.

Itis a further object of my invention to provide a new and improvedresistance unit which will maintain the value of itsresistancesubstantially constant over a long period of use.

It is a further object of my invention to provide a new and improvedresistance unit in which the contact resistance between the resistanceelement and its terminal structure is maintained at a constant and xedminimum.

It is a further object of my invention to provide a new and improvedresistance unit including a relatively high resistance frangibleresistance element in which the contact resistance between the frangibleresistance element and its terminal structure is maintained at aconstant and fixed f minimum.

It is a still further object of my invention to' provide anew andimproved resistance unit which may be applied in communication orksignalling circuits .without the production of noises or otherelectrical or audio disturbances.

invention to provide a new and improved resistance element suitable foruse in my improved resistance units which may be readily manufactured inlarge quantities with a small and uniform tolerance as to resistancevalue.

It is` another object of my invention to provide a new and improvedmethod of forming a resistance unit including a frangible resistanceele.- ment. l

`It is another object ofmy invention to provide a new and improvedmethod of forming a resistance unit by means ci which, the.contactresi'stancev between the resistance element and its terminalstructure is maintained at a constant and iixed minimum. -It is a stillfurther object oi my invention to provide a new and improved method vofforming a resistance unit including a frangible resistance element whichwill minimize the breakage of the vide a new and improved method offorming resistance elements suitable for use in my improved resistanceunit. v

This application is in part a-` continuation of my application SerialNo. 655,890, filed February 9, 1933.

For a better understanding Vof my invention, together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawings and its .scope willbe pointed out in the appended claims. y

Figs. 1, 1A and 1B are. respectively, a longitudinal section, a crosssection and top plan view yof ya resistance unit embodying my invention;

Figs. 1C and 1D areyrespectively, side and end 'elevational views of aresistor or resistance' elei ment with a lead applied thereto;

Figs. 2 and 2B are, respectively, a longitudinal` 20 section andacross-section of a. modication in which the conducting leads are in theform of metal lugs; E

Figs. 3, 3A andB are, respectively, a longitudinalsection of a unit ofmodied structure,`

a plan View when completed, and a cross-sectional View on the line B -B;Fig. 3, on enlarged scale,

' of a modification in which anv external helical connecting lead is.temporarily held in the molded mass and thereafter more or lesscompletely uncoiled;

Fig. a is a top plan view of the lower member of a mold by means ofwhich my improved method of forming resistance units may be practiced,while Fig. 5 is a longitudinal cross-sectional view along the lines D-'Dof Fig. 4. Fig. 4, on the other hand, is a view along the lines E-E of-Fig. 5. Fig. 6 is a cross-sectional view along the line C-C of Fig. 5;

Figs. 7 and 8, are, respectively, a cross-sectional o view and alongitudinal sectional view of a modi:

ed form of a mold particularly suitable for forming resistance unitsincluding frangible resistance elements;

Figs. 9, 10, 11, 11a, 12 and 13 illustrate the 45 several steps in thedevelopment of a complete f resistance unit as produced in the mold ofFigs.

7 and 8;

Figs. 14, 14a and 14h are, respectively, a topv plan View, an elevationand a cross-sectional view 50 along the lines G-G of Fig. 14 of a jigparticularly suitable for forming resistance elements for use in myimproved resistance unit, while Fig. 15 shows a detail of an assemblyof. my improved resistance elements.

55 Referring to Figs. 1, 1A and 1B, the resistor ruggedness, fullymechanically to protect the contained resistance element and associatedparts.

The insulating material constituting the casing 70 or envelope B may beanything suitable for the purposes in view. There may be employedlmoldable condensation products, such asvphenol-` formaldehyde resins,common among which -is bakelite; phenol-furfural resinoids; or -plastic75 compounds of rubber or equivalent, all moldable.

undejxi pressureat elevated temperatures. Or, for

cold molding, such material as asphaltic base compounds or equivalentsmay be utilized.

f The resistor R of the severalA figures of the draw-1 ings may comprisea core of insulating material 5 of cross-section of any suitable shape,commonly circular, of any suitable diameter and material. It may be inthe form of a illament, rod or tube, coated, either exteriorly or, whenin the form of a tube, interiorly with/any suitable conductive material,including nely divided metal, carbon and the like, to constituteconductively coated iilament or core of glass, ceramic and the like. Theresistance element R may, for example, be of the character described inmy prior Letters Patent No.

1,832,419, dated November 17, 1931. When the element R comprises a tubeinteriorly conductively coated, the terminals t will be of a form toenter the end of the tube and contact with its interior conductivecoating; or the element R. may comprise a molded body of any materialhaving suitable resistance characteristics.

The resistance elements of the types mentioned above may vary inresistance from values as low as a few ohms to as high as hundreds ofmeghorns.

As stated above, the contact resistance of such a resistance unit isailected bythe specific resistance of the resistance element.Furthermore,

this contact resistance is subject to substantial and. troublesomevariations. my invention, this diiculty is overcome by dis- -posing aplastic coating of c'onductive or rela-ll tively low resistance materialupon the portions of the resistance element to which the terminalstructures are attached. This coating is illustrated in detail in Figs.1, 1A, 1C and 1D of the drawings in which the coating material'is indicated by the reference d. The coatings d. formed on the resistance Rmaybe of any suitable mate:

rial having a relatively Alow resistance such as a 40 compositioncomprising `a nely divided metal or other conductor and a suitableplastic binder, although I prefer to use as this coating material acomposition of varnish or similar binder and graphitic or vamorphouscarbon. The preferred 4,5

coating material has a specic resistance` of the order of 0.03 ohms percentimeter cube. The coatings d may be applied in any suitable way, asby spraying, dipping,l painting, etc., although I prefer to spray thecoating on the resistance'ele- 50 ment R., as described more fully'hereinafter.

The leads L .are providedwith aterminal portion t which may be, forexample, of iiexible or readily malleable metal Wire or ribbon. Forexample, the terminal portion may be formed by attening one end of thelead'L and applying it under suitable pressure, by the ngers or atool,into at least sumciently rm engagement with `the end of element R tohold it in relative position suitable. for placing in'` a mold such ashereinafter 6o referred to. The pressure applied in molding theinsulating material upon the element R exerts,

upon each terminal t, pressure which is eiectiveto compress the terminalportion t about the coated section of the resistor R so that the coatingmaterial d iills the interstices of the resistance element R and theterminal portion t, establishing `a good electrical contact betweenthese two ele-4 ments. This pressure is more or less completelymaintained upon the solidication'of the molding 70 material, therebypermanently establishing arrV electrical contact-between the resistanceelement and its terminal structure having a constant and xed minimumvalue. The pressure of the molding operation is also eiective to bringlthe mold- 7.5

In accordance with 30 ing material into direct and intimate contact withall portions of the resistance unit establishing a rugged, protectiveand supporting envelope. It is preferable that the molding insulatingmaterial B should be of such material asA will wet during the moldingoperation, the leads or conductor elements L thereby effecting a closemoisture-proof connection or attachment consisting oi or comparable witha hermetic seal.

Whilethe resistance element R has been described as comprising aninsulating filament or rod covered with a 'conductive coating, thiselement may, if desired, be additionally coated with y a suitablefilm-like insulating coating oi any conventional type.

In Figs. 2, 2A and 2B the structure is generically the same ashereinbei'ore described. differing only as to the modification and thestructure of the leads. In this instance the external leads L2, of anysuitable conducting material, such, for example, as the leads L of Fig.1, have any suitable terminalstructure t2 embracing and contacting withthe resistor R. The leads L2 are in the form of lugs or more or lessrigid plates projecting beyond the exterior of the envelope B, andhaving any'suitable structure such as end hooks h, h by which they maybe hooked on to or otherwise attached to other conductors in the form ofposts, wires or the like.

In Figs. 3, 3A and 3B, the terminals t3, contacting with the resistor R,are in the form oi a conductor or wire wrappedvaround or coiled upon theends of the element R in electrical contact therewith. The wire mayextend beyond the exterior of the'block B proper in the form of astraight lead. r,'as illustrated, the wire continues to the exterior ofthe block B properfin the form of a coil or helix c, or otherwisesubstantially compactly arranged, and molded in a temporary lug aintegral with the envelope B proper. 'I'he material of the lug a illlsthe interior of the coil or compactly arranged conductor c, andpreferably extends between neighboring turns or convolutions thereof,and in some lnstances, as indicated in Figs. 3 and 3B, may extendsomewhat outwardly beyond the conductor c. After molding the structureinto the form shown in Fig. 3, the material of the-lug a' being ofrelatively small dimensions and more or less readily frangible, isbroken oi! from the conductor c and envelope B, whereupon the wire c maythen be drawn out substantially axially yielding a more or less straightor undulating ilnal lead Ll, Fig. 3A.

My invention also comprises improved methods of forming resistance unitsof the type described above. In the conventional methods of moldinginserts, suchas the resistance elements R in an insulating medium, theinsert to be molded is rigidly mounted in a chamber or cavity ofthemold, together with a quantity of the molding compound. These elementsare then subjected to heat and pressure. In the molding process thereare ordinarily developed substantial unbalanced pressures due to thefact that the change in volume oi the molding material is ordinarily oithe order o! 3 or 4 to l, and due to the impossibility of exactlydistributing the mass ot molding materlal uniformly with respect to theinsert. Also, the heating' is progressive Irom the parts of the moldingmaterial directly in contact with the hot mold to' those portionsl inintimate contact withv the insert, causing wide variations in theviscosity oi the molding material. These unbalanced pressures tend tocause a breakage. of the inserts which may become a serious problemparticularly in case the inserts are of a irangible nature, as in thepreferred form of my resistance element. This tendency to breakageisfurther aggravated by the fact that the molding pressure is generally'applied at right angles to the length 'of the" insert. If the ratio oi'length to diameter of the insert is great. as is often the case,particularly with the type of resistance element described above, arelatively small unbalanced pressure is sufllcient to cause' a breakageoi the insert. As an example, my invention has been utilized to mold aresistance element comprising a glass nbre-0.04 `inches in diameterand.2 inches long.

My present invention embraces an improved method o1' molding resistanceunits which overcome the above-described diillculties and makes themolding operation of very irangible elements a simple, economical andpractical procedure.

In Figs. 4, 5 and 6 is illustrated one of various mold structures bymeans of which my improved method of forming resistance units may bepracticed. In the lower mold member i is formed a pocket or cavity 2 ofthe length and breadth oi! the unit to be formed, and of a depth whichis a fraction, practically one-half, of the depth of the unit to bemolded. Extending from one side of the cavity 2 are channels or grooves3 to receive the terminals or leads L of the resistance element.Adjacent the comers of the member i are upstanding posts or pins 4, heldby screws,

rods or equivalent velements 5; the middle mold element 8 is providedwith holes, receiving the posts 4, and whose inner wall forms part ofthe end and side wall structure registering with the like walls of thecavity 2. The plunger or upper mold member l, also provided with holesto receive posts 4, has a projecting lower portion entering into theopening into the middle member 6,- and whose bottom face I forms the topwall of the upper halt of the mold cavity, lforming with the cavity 2inthe member i a mold oi' the form and dimensions of the unit.

With the mold members 6 and l removed, a resistor R, having its leadsLattached thereto by terminal elements t which engage the -resistor Rabout the coatings d, isI placed in the position indicated, with theleadsL in the channels or grooves 3. Due to the thinness of the terminalportions t of the leads L, they are ilexible or easily bendable, so thatthe resistor R is accordingly flexibly held in place', within oradjacent the top surface of the bakelite or other molding powder in .thecavity 2. In certain instances, it may be desirable also to support theresistance element R upon an auxiliary strip or block 9 of moldingmaterial whichhas b een previously molded under heat and pressure.'I'his block 9 is preferably provided with slots or perforations illwhich are effective to key it to the main mass oi molding material andalso to give it a certain may be used to support the resistanoe'elementthe dimensions or volume of the finished casing B. The pressuredeveloped in the molding operation'causes the ilexible terminals t ofthe resistor R. to firmly grip or engage the resistor. about the coatedportions compressing the plastic coating d into the interstices 'of theresistance element and the terminals forming a good electrical contactof a substantially ixed resistance. As the molding material B sets, upontreatment with heat and pressure, this relatively low resistance contactls maintained at a substantially fixed value.

The resistance elements illustrated as subject to the molding operationof Figs. 4, 5 and 6 are similar to those illustrated in Figs. 1 and 2 ofthe drawings. As stated above. the thinness of the terminal portions tof the leads L gives the resistance element R a certain flexibility ofsupport which permits the element a limited freedom of motion so that itmay adjust its position in response to unbalanced pressures developed inthe molding operation, as described above, thus reducing breakage to anegligible factor. In Fig. 3, described above, is illustrated'anotherterminal structure for resistance elements effective to give theresistance element a similar flexible support for the molding operation.

In. certain cases where the resistance element to be molded isparticularly frangible or where the nature of thel molding operationdemands it. an auxiliary perforated block 9, as described,

intermediate the terminal supports, as illustrated l in detail in Fig.5'of the drawings. Thisauxiliary supporting block is preferably of thesame material as the main mass of molding material,

thus forming a substantiallyintegral envelope of ther reduced by forcing'the molding Vmaterial axially into the mold cavities containingresistance elements. The moldi apparatus of Figs. f v

ng -sents the deformed 'turn which ac tsvas a stop against the end ofthe resistor R.A`

7 and 8 is somewhat similar to that of Figs. 4, 5 and 6 and comprises alower mold member la having a plurality of mold cavities 2a,l anintermediate mold section la provided with mold cavities 2b registeringwith and complementary to the cavities 2a. The mold is also providedwith an upper mold element or plunger la having a pressure surface la.-for forcing the molding material B into the mold cavities. In thisarrangement, however, the molding material B is not placed in the moldcavities with the resistance elements to be molded. but the intermediateand communicating therewith at one end of the.

mold through ports i2. Inv these gures there is illustrated the moldingof resistance elements R provided with exible terminal structures LI'coaxial with the resistance elements and extending throughv grooves 3ain the end of the mold element ia. In the operation of this moldingapparatus-when heat and pressure are applied to ,the upper mold elementor plunger la, the moldstreams through the ports I2 into the moldcavities 2a-,2b in a direction parallel to the length of the frangibleresistance element R. The direction of the iiow of the molding materialis as indicated in the small arrows in Figs. 7 and 8. 5

The molding material may be introduced into each of the mold cavitiesthrough a. separate port, or two or more ports may supply the moldingcompound in parallel, as shown in Fig. '1 of the drawings. In thismethod of molding, the unbalanced pressures transverse tothe length ofthe frangible resistance elements `are substantially eliminated.

InFigs. 9 and l0 are illustrated the developmentof the preferred form ofthe resistance element for embodiment in my improved resistance unit. InFig. 9 is shown the resistance element R with the coatings d disposedupon its end portion. As stated above, these coatings arepreferably of amixture of varnish or other plastic binder and iinely divided carbon.After the coating, the elements are preferably treated at elevatedtemperatures for a period to partially harden the coating material.However, this heat treatment is stopped at such a point that it is stillquite soft compared to ordinaryl metallic conductors. The leads L4 arethen `formed with terminal portions t4 comprising substantially helicalcoils, and these coils are threaded on the relatively soft coatings ofthe element R. The 3o helical coil cuts its own thread-on the coated endmaking an intimate contact of very low rev sistance, irrespective of theresistance of the element itself. This contact resistance is stillfurther reduced in the molding operation which is effective to stillfurther embed the, turns of the helical coil into the coating material,and this low resistance contact is permanently maintained by the settingof the molding insulating material.

In the preferred form of the terminals t4, the turns .immediatelyadjacent the leads L4 are deformedso that the helical coils begin atapproximately the axis ofthe resistor element and the leads L4 arecoaxial with the resistor element.' These deformed turns act asautomatic stops lto limit the travel of the terminals-t4 as they are.threaded on the resistor element R. This is ilr lustrated more clearlyin Figs. 11 and 11a in which the portion e of the terminal structure t4repre- In the forming of resistance units of the type covered'by myinvention, the value of the resistance of the unit is dependent upon thedistance between the terminal structures, and 'it is important that thisdistance should not be varied by variations'encountered in the assemblyprocedure. This problem is also solved by the improved resistor elementof Figs. 9 and 10, provided only that the terminal coatings areaccurately spaced on the resistor element. As shown in more detail inFig. 12, if the terminals t4, due to inaccuracies of manufacture orassembly, extend beyond the coated portions of the resistor element, theprojecting portions f of these terminals are separated from the elementR by the thickness of the terminal coatings d so that the effectivelength of the resistor element is maintainedat the value g, as indicatedin Fig. l2. In Fig. 13 -0 is shown, in longitudinal section, thecompleted resistance unit embodying the preferred form of my invention.It will be noted that this unit embodies the auxiliary perforatedsupporting block 9 described above.

there is shown in Figs. 14, 14a and 14b a simple apparatus by means ofwhich this coating may be applied with great accuracy and facility. Thisapparatus or jig comprises the complementary .supporting members orracks I3 and Il maintained in alignment by means of pins or bolts I 5.

IThe supporting members I3 and I4 are formed regularly and accuratelyspaced openings I6, the distance between the openings corresponding tothe desired length of the resistor elements and the width of theopenings being approximately twice the width of a terminal. One of thesnpporting elements, for example, the member I 4, is provided with aplurality of longitudinal slots I'I of the proper dimensions to snuglyhold a length of resistance element. One such element R is shown asplaced in one of the slots of the apparatus. By filling the severalslots Il of this apparatus with resistance elements, the coatings d maybe applied by means of a spray gun with great rapidity and ease. Ifdesired, there may be provided severing apparatus .comprising aplurality of cutters, one of which is designated by the referencenumeral I8 of Fig. l5. Such an apparatus is effective to accuratelysever the several resistance elements at a single operation either bycutting, nicking or chipping, according to the physical properties ofthe particular --resistance element which is b eing utilized.

What I claim is:

1. In a resistor construction, in combination,

an elongatedresistance element, electrical conductive coatings on theVend portions of said element immediately adjacent the ends thereof,said,

coatings being concentric with said element and I in intimate contactwith said element, thereby providing an excellent electrical connectionbetween said element and said coatings, said coatings being of muchgreater electrical conductivity than said element, wire terminals havingportions encircling said coatings and proportioned to fit iirmly againstsaid coatings when pressure is exerted thereagainst, and a mass of solidelectrical Y insulating material completely encasing said element andthe encircling portions of said terminals and exerting pressurethereagainst so that said terminals are held firmly against saidcoatings to provide an excellent electrical connection between saidterminals and said coatings.

2. In a resistor construction, in combination, an elongated resistanceelement, electrical conductive coatings on the end portions of saidelement immediately adjacent the ends thereof, said coatings beingconcentric with said element and in intimate contact with said element,thereby to provide an excellentV electrical connection between saidelement and said coatings, said coatings having much greater electricalconductivity than said element, wire terminals having helical shapedportions encircling said coatings andproportioned to fit firmlythereagainst when pressure is exerted thereon, said terminals havingsub- "stantially straight portions extending away from said encirclingportions, and a solid mass of elecltrical insulating material completelyencasing ductive' coatings on the end portions of said elementimmediately adjacent the ends thereof, said coatings being concentricvwith said element and in intimate contact with said element, thereby toprovide an excellent electrical connection between said 'element andsaid coatings, wire terminals including portions encircling saidcoatings and proportioned to iit firmly thereagainst, portions of eachof said terminals extending inward` ly to engage the ends of saidelement to act as stops, and a solid mass of electrical insulatingmaterial completely encasing said element and the encircling portions ofsaid terminals to exert a pressure on said terminals and hold them infirm engagement with said coatings.

4. In a resistor construction, in combination, an elongated resistanceelement, electrical conductive coatings superimposed on the end portionsof said element immediately adjacent the ends thereof, said coatingsbeingconcentric with said element and in intimate contact with saidelement, thereby to provide an excellent electrical connection betweensaid -element and said coatings, said coatings having much greaterconductivity than said element, wire terminals comprising helical-shaped portions and substantially straight portions, the helical shapedportions encircling said coatings, said terminals being deformed at thejunctions of said straight portions and said helical portions tofomstops' in engagement with the ends of said element, and a mass ofelectrical insulating material completely eircasing said element and thehelical portions of said terminals to maintain said terminals in iirmengagement with said coatings thereby providing anv excellent electricalconnection between said terminals and said coatings.

5. In a resistor construction, in combination, an elongated resistanceelement having an irregular surface electrical conductive coatingsconcentrically superimposed on the end portions of said element andimmediately adjacent the ends thereof, said coatings comprising a binderfilling the irregularities in the surface of said element and havingparticles of conducting material suspended therein thereby t-o provide aconnection between said coatings and said element having a constantvresistance value, wire terminals encircling said coatings andproportioned to fit firmly against said coatings, and a solid mass ofelectrical insulating material completely encasing said element and theencircling portionsof said terminals to hold said terminals permanentlyand iixedly against said coatings whereby a connection havingy aconstant resistance value is provided between said terminals and saidcoatings.

6. In a resistor construction, in combination, an elongated elementformed from electrical insulating material, an electrical resistancecoating on said element comprising a binder having particles ofconducting material suspended therein, the surface of said coating beingirregular, electrical conductive layers on the end portions of saidelement immediately adjacent the ends thereof and Aconcentric with saidelement and superimposed on said coating, said layers comprng a binderfilling the irregularities in the surface of said element and havingconducting particles suspended therein, thereby forming an excellentelectrical connection between said coating and said layers, said layershaving much greater conductivity than said coating, wire terminalshaving portions encircling said layers and proportioned to rest nrmlythereagainst, and a solidmass of 6 t cocasse l.

electrical insulating material encasing said element and the encirclingportionsof said terminals to hold said terminals nrmly and immovablyagainst said layers thereby providing an excellent electrical connectionbetween said terminals and said layers.

7. In a resistor construction, incombination, an elongated resistanceelement having irreguf larities in the surface thereof, electricalconduc- 10 ,tive coatings onthe end portions oi said element immediatelyadjacent the ends thereof, said coatings being concentric with saidelement and illiing said irregularities in s aid element, therebyproviding an electrical connection between said 15 element and saidcoatings having a stable resistance value, terminals having' portionsencircling said coatings and proportioned to fit iirmly against saidcoatings, and a mass of solid electri- 'cal insulating materialcompletely encasing said l element and the encircling portions of saidterminals to hold'said terminals permanently and ilxedly against saidcoatings whereby a stable electrical connection is provided between saidterminals and said coatings. v- 8. In aresistor construction, incombination. an

elongated' resistance element, electrical conductive coatings on the endportions of said element' immediately adjacent the ends thereof, saidcoatings being in intimatepontact with said element therebyprovidingexcellent electrical connections between said element and saidlcoatings, said.

coatings being oi' much greater electrical conductivity than saidelement, wire terminals having portions in interi'itting and engagingrelation to said coatings to form connections with said ,ele-

ment and proportioned to t rmly against said 5 coatings when pressure isexerted against said ings being ot much greater electrical conductivity'than said element, wire terminals having portions in irteriittting andengaging relationto said ocat- 20 ings -totorm connections with said'element and proportioned to tit firmly against said coatings whenpressure is exerted against 'said connections. and a mass oi solidelectrical insulating material completely enclosing said element and the25,

relatively interiitting portions oi' said terminals and said element.said terminals having bendable ends of the unit tor attachment purposes,30

LD mslm4 nn. l

